Fluorinated oils and greases are employed as lubricants in demanding applications. A well-known class of fluorinated lubricants are the perfluoroalkylpolyether oils available as commercial products under the trade names KRYTOX® (E. I. du Pont de Nemours and Company, Wilmington Del.), FOMBLIN® (Ausimont, Milan, Italy), and DEMNUM® (Daiken Industries, Japan). It is found in practice that in oxygen containing environments, the perfluoroalkylpolyethers may undergo degradation at temperatures as low as 150° C., with concomitant corrosion of some metal surfaces such as aluminum, iron and alloys thereof. There is a need for lubricating oil that remains stable to oxidative degradation at elevated temperature, and prevents corrosion of a lubricated metal surface.
U.S. Pat. No. 3,069,401 discloses the reaction hexafluoropropene with vinylidene fluoride and an aliphatic compound selected from the group consisting of alcohols, ketones and carboxylic acid esters that served as chain transfer agent in the presence of an initiator such as di-t-butylperoxide, and optionally a solvent.
U.S. Pat. Nos. 5,350,878, 5,446,214, and 5,493,049 disclose low molecular weight cotelomers of hexafluoropropene with more reactive telomers, prepared at relatively low temperatures and pressures using chlorinated and brominated terminal telogens to limit the molecular weight of the product copolymers and to obtain liquid products with chlorinated and brominated terminal groups that limit the thermal stability of the products.
U.S. Pat. No. 2,446,214 discloses that few units of hexafluoropropene (HFP) are incorporated using perfluoroalkyl iodides as a terminal telogen. U.S. Pat. No. 2,446,214 discloses the use of gamma radiation for initiation. Such high-energy initiation can causes extensive branching and cross-linking, composition characteristics that are undesirable in oils.
Anolick et al., U.S. Pat. Nos. 5,478,905, 5,663,255, 5,637,663, and 6,133,389 disclose a continuous polymerization process comprising contacting a large excess of hexafluoropropylene with fluoro-olefins such as tetrafluoroethylene and vinylidene fluoride and a radical initiator under a pressure of about 41 to about 690 MPa, and a temperature above about 200° to about 400° C. to produce amorphous copolymers.
Oligomeric high HFP content copolymers have numerous potential uses for protection of surfaces and lubrication, but the use of monomeric chain transfer agent undesirably couples molecular weight control with composition. U.S. Pat. No. 6,767,626 discloses an adaptation of the process disclosed by Anolick et al. to prepare oligomeric liquids using certain monomers for molecular weight control. It is desirable to find a chain transfer agent that affords desirable productivity for producing oligomeric oils but that is preferably not incorporated into the polymer chain except as chain terminators.